JPH0980855A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To more accurately correct the attenuation quantity of a drum surface potential at each color developing position. SOLUTION: The attenuation quantity of the drum surface potential is accurately corrected by a potential sensor 12 for detecting the surface potential of a photoreceptor drum 1, a means for obtaining the correction quantity of a high voltage output level based on each color developing position, a means 30 for detecting an environment in the device main body and a means for correcting the aforesaid correction quantity in accordance with the environment in the device main body, then, each output level of appropriate grid bias and developing bias are decided, then, objective image density is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic color image forming apparatus such as a color copying machine or a color printer.

[0002]

2. Description of the Related Art In a color image forming apparatus in which developing positions of respective colors are different from each other, a photosensitive drum is uniformly charged by applying a predetermined grid bias of a primary charger, and laser light is irradiated to form an electrostatic latent image. , Development is performed at different positions for each color. In this process, it is necessary to control the grid bias and the developing bias in order to obtain the desired image density. However, when the portion of the photosensitive drum to which the predetermined grid bias is applied reaches the developing position, the drum surface potential is increased. Has changed, and the photosensitive drum is not always uniformly charged by applying the grid bias.

Therefore, in order to uniformly charge the photosensitive drum, ideally, a potential sensor may be attached to each developing position of each color to control the output level of the grid bias and the developing bias of each color. Since the cost is high, the conventional method is to correct the attenuation of the drum surface potential at the developing position of each color using a fixed value to determine the output level of the grid bias and the developing bias of each color. Has been taken.

[0004]

However, the amount of attenuation of the drum surface potential due to the developing position on the photosensitive drum differs depending on the environment around the drum and the degree of deterioration of the drum. There arises a problem that the bias level cannot be determined and the desired image density may not be obtained.

Therefore, a first object of the present invention is to provide a color image forming apparatus capable of more accurately correcting the attenuation amount of the drum surface potential at the developing position of each color.

A second object of the present invention is to provide a color image forming apparatus capable of determining an appropriate output level of a grid bias and a developing bias to obtain a desired image density.

[0007]

The above object is achieved by a color image forming apparatus according to the present invention. In summary, the present invention has a photoconductor on which a latent image is formed, and a plurality of developing means that respectively contain developers of different colors and develop the latent image, and the developing position for each color is different. In the color image forming apparatus, means for detecting the surface potential of the photoconductor,
It has means for obtaining a correction amount of the high voltage output level based on the developing position of each color, means for detecting the environment inside the apparatus main body, and means for correcting the correction amount for the high voltage output level according to the environment inside the apparatus main body. A color image forming apparatus characterized by the above.

According to another aspect of the present invention, there are provided a photoconductor on which a latent image is formed, and a plurality of developing means for accommodating developers of different colors and developing the latent image. In a color image forming apparatus with different developing positions,
It has means for detecting the surface potential of the photoconductor, means for obtaining the attenuation amount of the surface potential of the photoconductor, and means for correcting the high voltage output level based on the attenuation amount of the surface potential and the developing position of each color. There is provided a color image forming apparatus characterized by the above.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a color image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic configuration diagram of a color image forming apparatus equipped with a toner density control device according to the present invention.

The color image forming apparatus of the present embodiment comprises an upper digital color image reader unit 101 (hereinafter abbreviated as a reader unit), a lower digital color image printer unit 102 (hereinafter abbreviated as a printer unit), a reader unit 101 and a printer. Part 1
Image processing unit 103.

In the reader unit 101, a reflected light image from the original document obtained by placing the original document on the original platen glass 31 and exposing and scanning it with the exposure lamp 32 is a full-color image formed integrally with the RGB three-color separation filter by the lens 33. The light is focused on the sensor 34 to obtain a color separation image analog signal. This color-separated image analog signal is digitized through an amplifier circuit (not shown), processed by the image processing unit 103, and sent to the printer unit 102.

In the printer section 102, the photosensitive drum 1, which is an image carrier, is rotatably carried in the direction of the arrow in the figure. Around the photosensitive drum 1, a pre-exposure lamp 11 for initializing the surface of the photosensitive drum 1, a primary charger 2 for uniformly charging the surface of the photosensitive drum 1, and image information on the photosensitive drum 1 are provided. Laser exposure optical system 3 that forms an electrostatic latent image according to the above, a potential sensor 12 that detects the potential of the surface of the photosensitive drum 1, a color that develops the electrostatic latent image formed on the photosensitive drum 1 into a visible image. Fixed developing device 4 including four developing devices 4y, 4c, 4m, and 4Bk that store different types of developers (toners), on-drum light amount detection sensor 13 that detects the amount of toner on photosensitive drum 1, recording A transfer device 5 including a transfer drum 5a as a material carrier, and a cleaning device 6 for removing the developer remaining on the photosensitive drum 1 are arranged.

In the laser exposure optical system 3, the reader unit 1
The image signal from 01 is converted into an optical signal by a laser output section (not shown), the converted laser light is reflected by the polygon mirror 3a, and projected on the surface of the photosensitive drum 1 through the lens 3b and the mirror 3c. , An electrostatic latent image corresponding to the color image signal of each color is formed.

At the time of image formation in the printer unit 102, the photosensitive drum 1 is rotated in the direction of the arrow shown in the figure, first, the surface of the photosensitive drum 1 is neutralized and initialized by the pre-exposure lamp 11, and then the primary charger 2 is used to expose it. The surface of the body drum 1 is uniformly charged, and a light image is emitted for each separated color to form a latent image.

Next, a predetermined developing device is operated to develop the latent image on the photosensitive drum 1, and toner images based on resin are sequentially formed on the photosensitive drum 1. Each developing device 4y,
4c, 4m, and 4Bk are eccentric cams 24y, 24c, and 24.
By the operations of m and 24Bk, the developing operation is performed by approaching each of the separated colors alternatively.

Further, the developed toner image on the photosensitive drum 1 is composed of a recording material cassette 7a, 7b, 7c, an intermediate tray 22 or a recording material tray 7m, a pickup roller, a paper feed guide, a paper feed roller and the like. The image is transferred onto the recording material supplied to the position facing the photosensitive drum 1 via the transport system and the transfer device 5.

In this embodiment, the transfer device 5 faces the transfer drum 5a, the transfer charger 5b for transferring the toner image onto the recording material, and the adsorption charger 5c for attracting the recording material onto the transfer drum 5a. Adsorption roller 5g, inner charger 5
d, a recording material carrying sheet 5f made of a dielectric material is integrally stretched in a cylindrical shape in the peripheral opening area of the transfer drum 5a which is rotatably supported and has an outer charger 5e. Has been done. A dielectric sheet such as a polycarbonate film is used as the recording material carrying sheet (hereinafter referred to as a transfer sheet) 5f.

As the drum-shaped transfer device 5, that is, the transfer drum 5a is rotated, the toner image on the photosensitive drum 1 is transferred onto the recording material carried on the transfer sheet 5f by the transfer charger 5b.

In this way, a desired number of color images are transferred to the recording material that is adsorbed and conveyed to the transfer sheet 5f, and a full color image is formed.

In the case of forming a full-color image, when the transfer of the four color toner images is completed in this way, the recording material is separated from the transfer drum 5a by the action of the separation claw 8a, the separation push-up roller 8b and the separation charger 5h, and the heat is generated. The sheet is discharged onto the tray 10 via the roller fixing device 9.

On the other hand, after the transfer, the photosensitive drum 1 is subjected to the image forming process again after the residual toner on the surface is cleaned by the cleaning device 6.

Further, in order to prevent the powder of the transfer sheet 5f of the transfer drum 5a from being scattered and adhered, the oil of the recording material and the like, a backup that faces the brush 14 via the fur brush 14 and the transfer sheet 5f. The roller 1 via the brush 15 and the oil removing roller 16 and the transfer sheet 5f.
Cleaning is performed by the action of the backup brush 17 which faces 6. Such cleaning is performed before or after image formation, and at any time when a jam (paper jam) occurs.

Further, in this embodiment, the eccentric cam 25 is operated at a desired timing and the cam follower 5i integrated with the transfer drum 5a is operated,
The gap between the transfer sheet 5f and the photosensitive drum 1 can be arbitrarily set. For example, during standby or when the power is off, the transfer drum 5a and the photosensitive drum 1 are separated from each other.

Next, the surface potential control of the photosensitive drum, which is a feature of the present invention, will be described in detail.

In this embodiment, when the power is turned on, the drum surface potential control described below is performed to determine the output levels of the grid bias and the developing bias of the primary charger, that is, the high voltage output level. The drum surface potential control is performed in the order of (1) drum surface potential measurement and (2) determination of high voltage output level. Then, at the start of copying, (3) the high voltage output level is corrected and the corrected level is output.

(1) Measurement of Drum Surface Potential The drum surface potential was measured in the graph of FIG. 2 by setting the grid bias of the primary charger to -300 V (Vg1),-.
It is set to a two-level voltage of 700 V (Vg2), and the light portion potential V when the laser is turned on for each voltage at that time
L1 and VL2 and the dark potential Vd when the laser is turned off
1 and Vd2 are measured by the potential sensor 12. From these measured values, straight lines Vd and VL are obtained as shown in the graph of FIG.

(2) Determination of high voltage output level In the graph of FIG. 3, the straight lines Vd and VL obtained by the drum surface potential measurement, the target contrast potential Vcont,
Also, the grid bias Vg and the developing bias DC component Vdc are obtained from the potential Vback for removing the fog during copying. The relationship between Vd, VL, Vcont, Vback, Vg, and Vdc is represented by the graph in FIG. 3, and the values shown in Table 1 below are used for Vcont and Vback for each color.

[0029]

[Table 1]

The straight line Vdv in FIG. 3 is V at the point on the straight line Vd.
It is calculated by adding back. The grid bias Vg and the development bias DC component Vdc are the straight line Vdv and the straight line VL.
Is the target contrast potential Vcont.
To be equal to.

(3) Correction of high voltage output level The grid bias Vg and the developing bias DC component Vdc obtained by (1) and (2) are the potential sensor 1 on the photosensitive drum.
The optimum output level at the position 2 is the optimum high-voltage output level because the potential on the photosensitive drum changes during the rotation of the photosensitive drum at the developing position of each color where the actual development is performed. I can't say. Therefore, Vg and Vdc are corrected so that the optimum output level is obtained at each color developing position, and the corrected output levels Vg ′ and Vdc ′ are determined.

First, the corrected grid bias Vg 'is obtained by Vg' = Vg + δd + δe. It should be noted that δd is a correction amount due to different development positions of the respective colors. Further, δe is a correction amount for correcting δd depending on the environment around the photoconductor drum, and varies depending on the water content q (g / m ³ ) in the substrate obtained by the environment sensor at the start of copying. The values shown in Tables 2 and 3 below are used as δd and δe.

[0033]

[Table 2]

[0034]

[Table 3]

Next, as shown in the graph of FIG. 4, the corrected developing bias DC component Vdc 'is obtained from Vg' and the straight line Vdv.

As described above, by more accurately obtaining the drum surface potential at the developing position for each color, it is possible to determine the appropriate output levels of the grid bias and the developing bias, and thus obtain the desired image density. You can

Second Embodiment Next, a second embodiment of the color image forming apparatus according to the present invention will be described. The color image forming apparatus of the present embodiment, as shown in FIG. 5, serves as a potential sensor for detecting the potential of the surface of the photoconductor drum 1 on the downstream side of the primary charger 2 in the rotating direction of the photoconductor drum 1. Further, the first potential sensor 12a provided on the upstream side of the developing device 4y and the developing device 4Bk
The configuration is the same as that of the first embodiment except that the second potential sensor 12b provided immediately downstream of the second image sensor is provided. Therefore, the description of the configuration and the function of the color image forming apparatus will be omitted, and the present embodiment will be described. Only the surface potential control of the photosensitive drum, which is a characteristic part of the example, will be described.

In this embodiment, when the power is turned on, the drum surface potential control described below is performed to determine the output levels of the primary charger grid bias and the developing bias. The drum surface potential control is performed in the order of (1) drum surface potential measurement and (2) determination of high voltage output level. Then, at the start of copying, (3) the high voltage output level is corrected and the corrected level is output.

(1) Measurement of Drum Surface Potential The drum surface potential was measured in the graph of FIG. 2 by setting the grid bias of the primary charger to -300 V (Vg1),-.
It is set to a two-level voltage of 700 V (Vg2), and the light portion potential V when the laser is turned on for each voltage at that time
L1 and VL2 and the dark potential Vd when the laser is turned off
1 and Vd2 are measured by the potential sensor 12. From these measured values, straight lines Vd and VL are obtained as shown in the graph of FIG.

(2) Determination of high voltage output level In the graph of FIG. 3, straight lines Vd and VL obtained by drum surface potential measurement, target contrast potential Vcont,
Also, the grid bias Vg and the developing bias DC component Vdc are obtained from the potential Vback for removing the fog during copying. The relationship between Vd, VL, Vcont, Vback, Vg, and Vdc is represented by the graph of FIG. 3. For Vcont and Vback, the values shown in Table 1 above are used for each color.

The straight line Vdv in FIG. 3 is V at the point on the straight line Vd.
It is calculated by adding back. The grid bias Vg and the development bias DC component Vdc are the straight line Vdv and the straight line VL.
Is the target contrast potential Vcont.
To be equal to.

(3) Correction of High Voltage Output Level The grid bias Vg and the developing bias DC component Vdc obtained by (1) and (2) are optimum output levels at the position of the first potential sensor 12a on the photosensitive drum. As for the developing position of each color in which actual development is performed, it cannot be said that the high-voltage output level is optimum because the surface potential on the drum changes while the photosensitive drum rotates. Therefore, Vg and Vdc are corrected so that the optimum output level is obtained at each color developing position, and the corrected output levels Vg ′ and Vdc ′ are determined.

First, the corrected grid bias Vg 'is obtained by Vg' = Vg + δd. Here, δd is the correction amount of the attenuation amount of the drum surface potential due to the difference in the developing position of each color, and is determined as follows.

At the start of copying, the grid bias of the primary charger is set to a voltage of -500V, and the light portion potential when the laser is turned on is set to the first and second potential sensors 12a and 12a.
Measurement is performed by b, and the respective measured values Va and Vb are obtained. The correction amount δd is, as shown in FIG. 6, a distance ds between the first and second potential sensors 12a and 12b on the circumference of the drum, and a distance d between the first potential sensor 12a and each color developing position.
Is calculated by using the following equation: δd = (Va−Vb) × d / ds.

Next, as shown in the graph of FIG.
The corrected development bias DC component Vdc 'is obtained from Vg' and the straight line Vdv.

As described above, by more accurately obtaining the drum surface potential at the developing position for each color, it is possible to determine the appropriate output levels of the grid bias and the developing bias, and thus obtain the desired image density. You can

[0047]

As is apparent from the above description, the color image forming apparatus of the present invention has a means for detecting the surface potential of the photoconductor and a high voltage output level of the charging means and the developing means based on the developing position of each color. Of the drum surface at the developing position of each color by having a means for obtaining the correction amount of the above, a means for detecting the environment inside the apparatus main body, and a means for correcting the correction amount for the high voltage output level according to the environment inside the apparatus main body. By more accurately obtaining the potential, it is possible to determine the appropriate output levels of the grid bias and the developing bias, and thus it is possible to obtain the desired image density and obtain a high quality image.

Also in the color image forming apparatus according to another aspect, means for detecting the surface potential of the photoconductor, means for obtaining the attenuation amount of the surface potential of the photoconductor, the surface potentials of the charging means and the developing means. By having means for correcting the high voltage output level based on the amount of attenuation and the developing position of each color, the same function and effect as described above can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram illustrating a color image forming apparatus according to a first exemplary embodiment.

FIG. 2 is a graph showing the relationship between grid bias and photosensitive drum surface potential.

FIG. 3 is a graph showing a relationship between a grid bias and a development bias DC component.

FIG. 4 is a graph showing a relationship between a grid bias and a developing bias DC component.

FIG. 5 is a schematic configuration diagram illustrating a color image forming apparatus according to a second exemplary embodiment.

FIG. 6 is an explanatory diagram showing a relationship between a potential sensor and a developing position in Embodiment 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Primary charging device (charging means) 4y, 4c, 4m, 4Bk Developing device 12 Potential sensor 12a First potential sensor 12b Second potential sensor 30 Environmental sensor

Claims (2)

[Claims] 1. A photosensitive member on which a latent image is formed, a charging unit for charging the surface of the photosensitive member, and a plurality of developing units for accommodating developers of different colors and developing the latent image. In a color image forming apparatus having different developing positions for each color, a means for detecting the surface potential of the photoconductor and a correction amount for the high voltage output level of the charging means and the developing means are obtained based on the developing positions for each color. A color image forming apparatus comprising: a means, a means for detecting the environment inside the apparatus body, and a means for correcting the correction amount of the high voltage output level according to the environment inside the apparatus body. 2. A photosensitive member on which a latent image is formed, a charging unit for charging the surface of the photosensitive member, and a plurality of developing units for accommodating developers of different colors and developing the latent image. However, in a color image forming apparatus in which the developing position for each color is different, a means for detecting the surface potential of the photoconductor, a means for obtaining the attenuation amount of the surface potential of the photoconductor, the attenuation amount of the surface potential and each color A color image forming apparatus comprising: a charging unit and a unit that corrects a high-voltage output level of the developing unit based on a developing position.